Stimulating the brain’s alpha rhythm may take the edge off anxiety under stress

A single session of mild, rhythm-based brain stimulation modestly reduced immediate anxiety after a stressful task in healthy middle-aged and older adults, according to a study published in the Journal of Affective Disorders. The treatment did not change participants’ broader judgments about stress or most physical measures of stress, suggesting its effects may be limited to short-term emotional reactions.

Stress can trigger several different responses. A person may feel anxious, judge a situation as threatening, sweat more, or show changes in pupil size. A treatment could reduce the emotional feeling of anxiety without changing how stressful a person believes an event is.

The researchers focused on alpha brain rhythms, electrical patterns that occur roughly 10 times per second. Alpha activity has been linked with attention and the regulation of emotional information. Transcranial alternating current stimulation (tACS) uses electrodes placed on the scalp to deliver a weak electrical current that follows a particular rhythm.

The team was interested in whether stimulating the brain at the alpha frequency could help people regulate their emotional response to stress. They targeted the frontoparietal control network, which helps the brain direct attention and manage emotional reactions.

Led by Rubén Romero-Marín of the Autonomous University of Barcelona in Spain, the researchers studied 42 healthy adults (average age about 59; 16 women) drawn from the Barcelona Brain Health Initiative. Participants were randomly assigned to receive either active stimulation (22 people) or a sham procedure (20 people) that reproduced the electrodes and ramping sensations but did not deliver a sustained current. The active group received 20 minutes of stimulation at 10 Hz through electrodes placed over left frontal and parietal areas of the scalp.

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Participants completed a stress task before and after the intervention. They watched two circles moving around a screen. Whenever the circles collided, they received a mild electric shock to the hand, along with an unpleasant noise and a bright flash. The researchers measured state anxiety, perceived stress, brain electrical activity, skin conductance and pupil responses.

The clearest effect was found in state anxiety, which refers to how anxious a person feels at a particular moment. On a questionnaire scored from 20 to 80, anxiety scores in the active-stimulation group fell by 3.16 points after treatment. In the sham group, scores increased by 1.17 points. The difference between groups was statistically significant, though only narrowly. The researchers described the result as a “modest, selective reduction in stress-evoked state anxiety.”

The treatment did not change perceived stress appraisal. Participants did not appear to judge the stressful task as less demanding after active stimulation. This distinction suggests that the intervention may have influenced emotional reactivity rather than the way participants evaluated the situation.

The brain findings were more mixed. Resting brain activity did not show a reliable change in alpha power after stimulation. However, during the stress task, activity over the left frontal region showed a trend toward a larger increase in alpha activity in the active-stimulation group. The authors suggested this might reflect stronger regulation of emotional information while participants were under pressure.

Physical stress measures did not provide evidence of a specific stimulation effect. Skin conductance and pupil responses changed between the first and second sessions in both groups, which may have reflected learning or becoming accustomed to the task rather than the treatment itself.

The study has several important caveats. It involved only healthy adults, who generally had low anxiety levels, so the results may not apply to people with anxiety disorders. The sample was small, and technical problems further reduced the number of participants available for the physiological analyses. Also, the intervention consisted of only one session, and the researchers did not test another active frequency, so they could not determine whether the result was specific to alpha stimulation.

The study, “Reducing state anxiety with alpha-frequency transcranial alternating current stimulation,” was authored by Rubén Romero-Marín, Simon Fankhauser, Javier Solana-Sánchez, Ruben Perellón-Alfonso, Josep Maria Tormos-Muñoz, Luiz Pessoa, David Bartrés-Faz, Davide Cappon, Álvaro Pascual-Leone and Gabriele Cattaneo.